In this proposal, we describe a new pathway signaling neutrophil (PMN) influx and damage to the airways that may play a role as an initiator or cofactor for chronic inflammatory lung diseases such as cystic fibrosis (CF). We have previously demonstrated that proline-glycine-proline (PGP) peptides can cause a robust PMN influx into the airways of mice; this cellular specificity is due to structural relatedness to a receptor binding domain of CXC chemokines such as IL-8. The PI has shown that PGP is released from collagen by a stepwise process initially involving matrix metalloproteases (MMP)-8 and/or 9 with prolyl endopeptidase (PE) catalyzing the final reaction. Recently, the PI's lab has shown that PE is found in neutrophils and stimulated PMNs, when incubated on collagen, can cause notable PGP generation. Although work from the PI's group has demonstrated that PGP is found in CF airway secretions, the impact of PGP peptides in augmenting inflammatory responses in CF lung disease is not currently known. This grant application aims to address this by first investigating the impact of CXC ligands (including PGP and N-(-PGP) as a novel mechanism for the generation of PGP in ex vivo studies and further examining the specific intracellular pathways utilized for protease release from neutrophils. Then, these observations will be taken to a unique mouse model of CF lung disease, the (-ENaC overexpressor mouse (Specific Aim 2), to determine the impact of components of this inflammatory pathway on the phenotype and inflammatory response observed in this murine model. Determination of these fundamental pathways driving protease regulation/release have important implications to patients with chronic inflammatory disease, such as CF, where inflammatory stimuli such as CXC chemokines, are in increased abundance even during periods of disease stability. Our preliminary evidence suggests that at the beginning of an inpatient CF exacerbation, PGP levels are elevated but do decline by the end of hospitalization. However, even with this clinical improvement, PGP levels are still elevated compared to non-disease controls, suggesting that there continues to be ongoing inflammation in these airways. In the final aim of this proposal, we examine if clinically stable CF individuals have elevated levels of PGP and proteases in both sputum and serum. If so, it is possible that their elevation and persistence may predict the development of future disease exacerbations, serving as a unique biomarker for CF lung disease. The findings generated from these aims may have profound translational implications not only to CF lung disease but potentially to other neutrophilic inflammatory conditions.